Build Status

Current Release 2.12.1

Description

Optimized JSON (Oj), as the name implies, was written to provide speed optimized
JSON handling. It was designed as a faster alternative to Yajl and other
common Ruby JSON parsers. So far it has achieved that, and is about 2 times faster
than any other Ruby JSON parser, and 3 or more times faster at serializing JSON.

Oj has several dump or serialization modes which control how Ruby Objects are
converted to JSON. These modes are set with the :mode option in either the
default options or as one of the options to the dump method. The default mode
is the :object mode.

:strict mode will only allow the 7 basic JSON types to be serialized. Any
other Object will raise an Exception.

:null mode replaces any Object that is not one of the JSON types with a JSON null.

:object mode will dump any Object as a JSON Object with keys that match the
Ruby Object's variable names without the '@' prefix character. This is the highest
performance mode.

:compat mode attempts to be compatible with other systems. It will serialize any
Object, but will check to see if the Object implements an to_hash or to_json
method. If either exists, that method is used for serializing the Object.
Since as_json is more flexible and produces more consistent output, it is
preferred over the to_json method. If neither the to_json or to_hash
methods exists, then the Oj internal Object variable encoding is used.

Compatibility

Ruby

Oj is compatible with Ruby 1.8.7, 1.9.2, 1.9.3, 2.0.0, 2.1, 2.2 and RBX.
Support for JRuby has been removed as JRuby no longer supports C extensions and
there are bugs in the older versions that are not being fixed.

Rails

Although up until 4.1 Rails uses multi_json, an issue in Rails causes ActiveSupport to fail to make use Oj for JSON handling.
There is a
gem to patch this for
Rails 3.2 and 4.0. As of the Oj 2.6.0 release the default behavior is to not use
the to_json() method unless the :use_to_json option is set. This provides
another work around to the rails older and newer behavior.

In version Rails 4.1, multi_json has been removed, and this patch is unnecessary and will no longer work.
Instead, use the oj_mimic_jsongem along with oj in your Gemfile to have Oj mimic the JSON gem and be used in its place by ActiveSupport JSON handling:
gem 'oj'
gem 'oj_mimic_json'

Proper Use

Two settings in Oj are useful for parsing but do expose a vulnerability if used from an untrusted source. Symbolized
keys can cause memory to be filled since Ruby does not garbage collect Symbols. The same is true for auto
defining classes; memory will also be exhausted if too many classes are automatically defined. Auto defining is a useful
feature during development and from trusted sources but it allows too many classes to be created in the object load
mode and auto defined is used with an untrusted source. The Oj.strict_load() method sets and uses the most strict and safest options. It should be used by developers who find it difficult to understand the options available in Oj.

The options in Oj are designed to provide flexibility to the developer. This flexibility allows Objects to be serialized
and deserialized. No methods are ever called on these created Objects but that does not stop the developer from calling
methods on them. As in any system, check your inputs before working with them. Taking an arbitrary String
from a user and evaluating it is never a good idea from an unsecure source. The same is true for Object attributes as
they are not more than Strings. Always check inputs from untrusted sources.

Simple JSON Writing and Parsing Example

Alternative JSON Processing APIs

Oj offers a few alternative APIs for processing JSON. The fastest one is the Oj::Doc API. The Oj::Doc API takes a
completely different approach by opening a JSON document and providing calls to navigate around the JSON while it is
open. With this approach, JSON access can be well over 20 times faster than conventional JSON parsing.

The Oj::Saj and Oj::ScHandler APIs are callback parsers that
walk the JSON document depth first and makes callbacks for each element.
Both callback parser are useful when only portions of the JSON are of
interest. Performance up to 20 times faster than conventional JSON is
possible. The API is simple to use but does require a different approach than
the conventional parse followed by access approach used by conventional JSON
parsing.